(+)-CC-1065 (1) and the duocarmycins 2 and 3, illustrated in FIG. 1, are natural products having antitumor antibiotic activity through the alkylation of DNA. (Hanka, L. J., et al. J. Antibiot. 1978, 31, 1211; Yasuzawa, T., et al., Chem. Pharm. Bull. 1995, 43, 378; and Takahashi, I., et al., J. Antibiot. 1991, 44, 1045.) Prior studies have shown that the natural products can withstand and may benefit from significant structural modifications to the alkylation subunit and that the resulting agents retain their ability to participate in the characteristic sequence-selective DNA alkylation reaction. (Boger, D. L., et al., Chem. Rev. 1997, 97, 787.) These structural modifications, and the definition of their effects have served to advance the understanding of the origin of the catalysis of the DNA alkylation reaction by 1-3. (Harper, D. E. J. Am. Chem. Soc. 1994, 116, 7573; and Warpehoski, M. A., et al., J. Am. Chem. Soc. 1995, 117, 2951.)
These structural modifications have also served to advance the understanding of the origin of the DNA sequence selectivity of 1-3. (Warpehoski, M. A. In Advances in DNA Sequence Specific Agents; Hurley, L. H., Ed.; JAI: Greenwich, Conn., 1992; Vol. 1, p 217; Hurley, L. H. and Draves, P. In Molecular Aspects of Anticancer Drug-DNA Interactions; Neidle, S. and Waring, M., Eds.; CRC: Ann Arbor, 1993; Vol. 1, p 89; and Aristoff, P. A. In Advances in Medicinal Chemistry; JAI: Greenwich, Conn., 1993; Vol. 2, p 67). Two models have been proposed to explain the mechanism of the DNA sequence selectivity of 1-3. One model proposed by Boger states that the DNA sequence selectivity of 1-3 is determined by the AT-rich noncovalent binding selectivity of these agents and their steric accessibility to the adenine N3 alkylation site. (Boger, D. L., et al., Angew. Chem., Int. Ed. Engl. 1996, 35, 1439; and Boger, D. L., et al., Biorg. Med. Chem. 1997, 5, 263.) This noncovalent binding model accommodates and explains the reverse and offset 5 or 3.5 base-pair AT-rich adenine N3 alkylation selectivities of the natural and unnatural enantiomers of 1 (Boger, D. L., et al.,. J. Am. Chem. Soc. 1990, 112, 4623; and Boger, D. L., et al, Bioorg. Med. Chem. 1994, 2, 115) and the natural and unnatural enantiomers of 2-3. (Boger, D. L., et al.,. J. Am. Chem. Soc. 1993, 115, 9872; and Boger, D. L., et al.,. J. Am. Chem. Soc. 1994, 116, 1635.) This noncovalent binding model also requires that simple derivatives of the alkylation subunits exhibit alkylation selectivities distinct from the natural products. It also offers an explanation for the identical alkylation selectivities of both enantiomers of such simple derivatives (5'-AA&gt;5'-TA), and the more extended AT-rich selectivity of the advanced analogs of 1-3 corresponds nicely to the length of the agent and the size of the required binding region surrounding the alkylation site. This model is further supported by the demonstrated AT-rich noncovalent binding of these agents. (Boger, D. L., et al., Chem.-Biol. Interactions 1990, 73, 29; and Boger, D. L., et al., J. Org. Chem. 1992, 57, 1277.) The model is also supported by the correspondence between the observed preferential noncovalent binding and the observed DNA alkylation of these agents. (Boger, D. L, et al., Bioorg. Med. Chem. 1996, 4, 859.) Also the observation that the characteristic DNA alkylation selectivity of these agents does not require the presence of the C-4 carbonyl or even the activated cyclopropane provides further support for the model, (Boger, D. L.et al., J. Am. Chem. Soc. 1991, 113, 3980.; and Boger, D. L., et al. Proc. Natl. Acad Sci. U.S.A. 1991, 88, 1431.) The accuracy of this model is further demonstration of the complete switch in the inherent enantiomeric DNA alkylation selectivity that accompanied the reversal of the orientation of the DNA binding subunits with reversed versus extended analogs of the duocarmycins. (Boger, D. L., et al.,. J. Am. Chem. Soc. 1997, 119, 4977; Boger, D. L., et al., J. Am. Chem. Soc. 1997, 119, 4987; and Boger, D. L., et al., J. Am. Chem. Soc. 1995, 117, 1443.)
The above AT-rich noncovalent binding model contrasts with an alternative proposal in which a sequence-dependent backbone phosphate protonation of the C-4 carbonyl activates the agent for DNA alkylation and controls the sequence selectivity. (Hurley, L. H. J. Am. Chem. Soc. 1995, 117, 2371.)
Structural studies of DNA-agent adducts, .sup.17-19 the C-4 carbonyl of the natural products projects out of the minor groove lying on the outer face of the complexes potentially accessible to the phosphate backbone. (Lin, C. H., et al., J. Mol. Biol. 1995, 248, 162.; and Smith, J. A., et al., J. Mol. Biol. 1997, 272, 237.) However, the relative importance of the C-4 carbonyl positioning to the properties of these agents has not be determined.
What is needed is a series of analogs of (+)-CC-1065 (1) and the duocarmycins 2 and 3 which exploit the AT-rich noncovalent binding model and which retain their DNA binding and alkylating activity and selectivity. What is needed is series of analogs of (+)-CC-1065 (1) and the duocarmycins 2 and 3 which incorporate of iso-CI and iso-CBI (6 and 7). Iso-CI and iso-CBI (6 and 7) are analogs of the CI and CBI alkylation subunits 4 and 5 wherein the key C-4 carbonyl is isomerically relocated to the C-6 or C-8 positions, now ortho to the cyclopropane, as illustrated in FIG. 2. If the AT-rich noncovalent binding model is correct, the relocated carbonyls of iso-CI and iso-CBI (6 and 7) would project into the minor groove inaccessible to the phosphate backbone if participating in an analogous adenine N3 alkylation reaction.